Unitized body structure for earth moving apparatus

ABSTRACT

An earth moving apparatus, such as a self-loading scraper, where the scraper body, primarily the side walls, is made of prefabricated panels constructed of rectangular tubes joined in side-by-side relationship by straight line fillet welds producing a high strength, rigid unitized body lending itself to automatic welding fabrication.

1 1 3,732,36 14 1 May15,1973

1,1111% tates $19111 1 91 Stuller et :11.

[54] UNHTIZED BODY STRUCTURE FOR EARTH MOVING APPARATUS [75] Inventors: Howard E. Stuller; Glenn E. Walse ,555,71O Erickson et 211....

3,471,951 De Boeuf et al......

5/1964 Collins et al.

both of Lubbock, Tex.

Clark ....296/28 M ....296/28 M ...296/28 M X 3,097,877 7/1963 Erlandsen 2,642,817

6/1953 Goldberg 1/1968 [73] Assignee: Equipment Company,

Buchanan, Mich.

Oct. 4, 1971 Hanifan...... 2,994,139 8/1961 Carston.............................

[22] Filed:

Primary Examiner-Robert E. Pulfrey Eugene H. Eickholt [2]] Appl. No.: 185,986

Assistant Examiner that L T wd a C O m A S R Ur .n T te S mo.

C A Pw h a n nt y hw

m 1 ep l 5 nu A [As Mw w m m nmn3 m m .U 7 "um O a 7 el. NUSM u m d2 Stud UhF 1]] 2 8 555 [.ll.

walls, is made of prefabricated panels constructed of [5 6] References Cited rectangular tubes joined in side-by-side relationship by straight line fillet welds produc rigid unitized body lendin fabrication.

ing a high strength, g itself to automatic welding UNITED STATES PATENTS 13 Claims, 9 Drawing Figures PATENTEDMY 1 5191s 3'. 732,636

SHEET 1 OF 2 INVENTORS HOWARD E. STULLER ATTORN EY GLENN E. WALSER V PATENTE MAY 1 5197s SHEET 2 OF 2 INVENTORS HOWARD ATTORNEY UNITIZED BODY STRUCTURE FOR EARTH MOVING APPARATUS BACKGROUND OF THE INVENTION 1. Field of the Invention The invention relates generally to earth moving appa- .ratus and particularly to a self-loading scraper body construction. Self-loading scrapers are well known. The main parts will usually comprise an elevatorin the front to assist in loading dirt into the scraper bowl. An end gate at the rear of the bowl slideson a stationary floor for ejecting or dumping the dirt through a bottom opening. A rolling door normally covering the opening is retracted when the end gate pushes the dirt forwardly. The invention, however, is not limited to selfloading scrapers and is believed equally useful for other types of earth moving equipment where heavy hauling loads over rugged terrain are encountered.

2. Description of Prior Art Heretofore scraper bodies have been built piecemeal; see for example. US. Pat. No. 2,988,832 of June 20, 1961 to LB. Hancock for a generalized showing of a known type of scraper body. Hand welded heavy box framing provides the main structural support. Thick side and floor plates are welded to the framing to provide the interior surfaces of the scraper body or bowl. Numerous weldments of relatively massive cross section are required. It is impossible to relieve stresses completely in all such weld locations and the opportunity for stress corrosion cracking and weld distortion is great.

Also, hand welding speeds are at best about six to eight inches per minute and consequently many hours are required to build a scraper'body.

Moreover, sub-assemblies which attach to the scraper body, such as the main blade support frame, yoke arm pivot blocks, and rolling door trackways, require separate weld operations at various locations on the scraper body. These sub-assemblies produce intricate joints between heavy and light material sections creating a further problem of weld distortion and also requiring considerable hand welding time.

Furthermore, sub-assemblies, such as the main blade support frame are made up of complicated metal shapes which in themselves require numerous heavy weldments. For example, the support frame for the main blade may have a top plate to which the main blade is bolted. Underneath are numerous angles and gussets providing the necessary rigidity for mounting the blade and for supporting the scraper side walls. Frame type construction of scraper bodies has proved costly in terms of labor, results in a relatively heavy body for the required strength, and is subject to built in stress points and weld distortion.

SUMMARY OF THE INVENTION A unitized scraper body is constructed of prefabricated panels. The panels are formed of rectangular tubes having a neutral axis at the geometric center. When joined in side-by-side relationship the tubes provide joints forming parallel straight line fillet welds ideally suited for automatic welding. The edges of adjacent tubes are joined producing a balanced weld about the neutral axis of the tube tending to reduce angular distortion to zero. The resulting tubular panel provides maximum strength with limited material thickness and weight and having minimum built-in stress concentrations.

In the case of panels for the side walls of the scraper, the upper tubes are shorter than the intermediate tubes providing openings on each side of the scraper for insertion ofa pair of pivot block inserts. Yoke arms trailing from the tractor are pivoted on the pivot block inserts for supporting the scraper.

Also, the lower tubes of the side panels are shorter and have their front ends inclined downwardly and rearwardly. A pair of side plate inserts abut on the front ends of the lower tubes for mounting the main blade.

The main blade support frame is itself a tubular subassembly, the ends of which abut the side plate inserts in a fashion establishing the proper angle with the ground of the main blade and presenting peripheral straight line welds for securing the blade frame to the side plate inserts.

Carrying out the unitized body construction still further, trackways for the rollers at opposite ends of the rolling door are fabricated with each side panel. Longitudinally extending cut-outs in the lower tubes of each side panel provide openings to receive channel elements forming the roller trackways.

Where the rolling door has a tubular construction also, the front edge of the door has a sleeve member secured thereto providing laterially spaced hinge locations for pivotally mounting a strike-off blade.

As used herein, the term unitized shall refer to a unitary body structure characterized by the absence of a frame where such body is constructed of tubular panels and components which themselves provide the rigidity and strength needed to withstand the stresses encountered during operating conditions.

The present unitized body construction, in addition to lending itself to high production automatic welding techniques, has a greater section modulus per panel wall with less material thickness and weight than previous frame and plate type wall constructions, is less subject to weld distortion, has fewer high stress locations minimizing joint failures and stress corrosion cracking problems and, owing to the double wall construction is less subject to damage, i.e., the outer tube wall may become dented without affecting the inner tube wall.

These and other features of the invention will be come more apparent by reference to the following detailed description which proceeds with a description of the drawings.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a side elevational view of a self-loading tractor scraper in which the scraper has a unitized body construction in accordance with the preferred embodiment of the invention;

FIG. 2 is an isolated perspective view of the scraper body looking in from the left quarter position showing details of the unitized body construction;

FIG. 2a is a fragmentary view of the left front corner of the scraper body taken along line 2a2a of FIG. 2;

FIG. 3 is a vertical sectional view through the left side panel of the scraper body taken along line 33 of FIG.

FIG. 4 is a longitudinal sectional view taken through the floor of the scraper body along line 4-4 of FIG. 2 showing the rolling door in the forward position with the strike-off blade raised in the closed condition;

FIG. 4a is a fragmentary bottom view of the strike-off blade frame;

FIG. 5 is a cross-sectional view of the main blade taken along line 55 of FIG. 2;

FIG. 5a is a fragmentary bottom view of the main blade; and

FIG. 6 is a schematic top view of an automatic welding setup depicting automatic welding fabrication of a side panel for the scraper body.

DESCRIPTION OF PREFERRED EMBODIMENT FIG. 1 depicts an earth moving apparatus, or more specifically, a self-loading scraper 10 towed by a tractor 12. The scraper 10 has a yoke 13 pivotally connected at 14 to the tractor permitting articulation of the scraper relative to the tractor. Arms 15 pivotally connect at the front of the scraper body 16 such that the scraper may be lowered and raised by action of lift cylinders 17, one connected adjacent each side of the scraper body. A fixed main blade 18 is rigidly mounted on a blade frame extending across the front of the scraper body and joined at each end to a side plate insert 19 mounted in the side walls 25. The blade 18 has a downward inclination suitable for engagement with the ground when the scraper is lowered to make a cut. An elevator 20 is mounted in front of the body 16 on mounts 23 to break loose earth material in advance of the main blade 18 and assists in filling the scraper in a known manner. The scraper is supported at the rear on ground engaging wheels 21 mounted on an axle which is supported on a trailing sub-assembly 22. An end gate 24 extends across the back of the scraper body between the side wall 25 and slides on a fixed floor portion 26. A rolling door 27 is suspended at each end on rollers 28 below the fixed floor portion 26. The rollers 28 travel in longitudinal trackways 29 on each side of the scraper body 16. An ejection mechanism 30 is supported on the sub-frame assembly 22 and may be actuated to retract the door 27 and push the end gate 24 forwardly to expel the earth material. A strike-off blade 32 is hinged on the front of door 27 and pivots downwardly as the door retracts to spread or level the earth material beneath the scraper as it moves forwardly dumping the load as it goes.

It should be noted that scraper 10 has four major stationary body components comprising a pair of side walls 25, stationary floor 26, and the main blade frame 45. Principal movable body components comprise the end gate 24, rolling door 27, and strike-off blade 32.

Referring to FIGS. 2 and 3 it will be seen that side walls 25 are each prefabricated panels formed of a plurality of rectangular tubes 40 extending longitudinally parallel to the centerline of the scraper body 16. Each tube 40 is in vertical abutting side-by-side relationship, with the inner and outer walls 41-42 of the tubes 40 forming a plurality of co-planer segments defining the interior and exterior surfaces of the panels. In the preferred embodiment of the invention each tube 40 has a 2 X 12 inch rectangular cross section having its neutral axis at the center, however, other dimensions may be used.

The side walls 25 are joined at the bottom by a stationary floor 26 and by a cross tube 43 adjacent the top near the rear of the scraper body. The stationary floor 26 is itself a tubular panel construction similar to the side panels, only in the floor area, the rectangular tubes are laid horizontally side-by-side with the long axis extending transversely of the centerline of the scraper body. Small bridging welds 34 are applied at laterally spaced locations between the tubes so that the end gate 24 will ride smoothly over the joints. The floor panel abuts at the opposite ends with the inner sides of the side panels providing a straight line peripheral weld at each end location.

The unitized panels provide a prefabricated structure having minimum material thickness with a greater section modulus and strength-to-weight ration than known box frame and plate body construction. It is important that at least each of the side walls be made of the tubular panels so as to provide the necessary strength to permit the elimination of a frame, however, the strength considerations for the unitized body are also carried over in the design of other stationary body components which cooperate in the overall design, as will be seen hereinafter.

The lower corners of each side wall 25 each receive a side plate insert 19 for mounting a main blade frame 45. Each side plate insert 19 also provides a forwardly extending mounting lug 49 for connection with lift cylinders 17 on the opposite sides of the scraper. FIGS. 5-5a show the main blade frame 45 which comprises a tubular element 50 spaced from and extending parallel to the main blade 18. Tubular element 50 has spaced upper and lower walls 51-52. A top plate 53 extends lengthwise of the tubular element and projects laterally from the upper wall 51 in a downwardly inclined direction for carrying the main blade 18 at a suitable angle for engagement with the ground. A bottom plate 54 extending lengthwise of the tubular element 50 is joined at the rear to the lower wall 52 and extends laterally on an angle joining adjacent the outer end of the upper plate 53. A row of openings 55 provide access for bolts holding on the main blade 18. The bottom plate 54, top plate 53 and tube 50 abut at their opposite ends with the inner surfaces of the side plate inserts 19 received in the lower openings in the side walls 25, thus defining with the side plate inserts generally straight line, peripheral welds around the blade frame 45. The blade frame 45 thus carries out the unitized body concept in that it employs a tubular structure having a greater strength-to-weight ratio and section modulus than known blade fabrications requiring the use of gussets to support the blade. The blade frame mounting locations are particularly critical points in the structure inasmuch as heavy loads are acting at these locations. For example, the earth material in the bowl, which may be several tons, tends to spread the side walls, placing the blade frame in tension. The action of the blade 18 in making a cut produces a considerable additional force acting on the blade frame. The forces transmitted by the lift cylinders 17, which attach at the lugs 49 on side plate inserts 19 are, in part, also acting on the blade frame. All of these forces tend to concentrate very high stresses at the ends of the blade frame. Ordinarily reinforcing plates are required in these areas which require heavy weldments creating considerable weld shrinkage and local distortion problems which are largely eliminated with the unitized body construction.

Referring to FIG. 2a, the connection between the blade frame 45 and side plate inserts 19 is shown, it being understood that the mounting on the opposite ends is identical. A side plate 57 is shaped to fit in the opening at the lower corner of the side wall 25. The lower tubes 40 have a front inclined end 58 which abuts a flange portion 59 projecting inwardly along the rear of the side plate 57. The flange portion 59 closes the open front end of the lower tube 40. The blade frame 45 abuts against flange portion 59. The slope of the inclined end 58 of the lower tubes 40 is thus at an angle which causes the blade frame to assume a proper downward inclination with respect to the ground as depicted in FIG. 5. The side plate 57 and flange portion 59are of relatively heavy section as compared to the wall thickness of the tubes 40 and present ideal fillet welds for mounting the relatively heavy blade frame.

Another high stress area is the mounting location of each yoke arm with the side walls 25. The pivot block inserts 46 have bearings 47 for attachment of the yoke arms 15 and are inserted in openings at the upper corners of the side walls. The upper tube 40 of each side wall has a front inclined end 60 (FIG. 2) in abutting relationship with the rear inclined end of each pivot block insert which closes the open end of the tube. The open front ends of the intermediate tubes 40 are closed by plates 62.

Thus, at the points of greatest stress, the unitized body 16 employs structural inserts which can be integrated into the side panels without complicated plates and support gussets normally required in these areas. The number of weldments is reduced and the joints are primarily straight line, ideal fillets tending to reduce weld metal deposition and weld penetration to a minimum.

The formation of the trackways 29 in the side panels is another unique feature of the unitized body construction. Heretofore, with scraper construction of the frame and plate type, the trackways have been fabricated of angles placed along the lower portion of the side plates. Such a construction, for example, is shown in U.S. Pat. No. 2,958,832 previously mentioned. While such a trackway is entirely satisfactory, the present utilized body concept makes possible the formation of a trackway as an integral part of each side panel. As shown in FIG. 3, the outer wall 42 of each lower tube 40 has a longitudinally extending cut out 64. A channel member 65 having a web 66 and end legs 67-68 is secured in each cut out 64. The lower leg 68 has a wear strip 69 on which the rollers 28 travel. The recessed mounting of the rollers 28 also tends to protect them from damage and wear against the side walls of the cut made by the main blade 18.

In addition to the stationary body components, the movable body components also preferably carry out the unitized body concept, although this is not essential from a structural strength standpoint to permit elimination of a frame, but rather for production considerations because of the applicability of automatic welding techniques.

FIG. 4 is a longitudinal sectional view showing the rolling door 27 and strike-off blade 32. The stationary floor 26 is secured between the side walls 25 at the rear and the rolling door is suspended on the rollers 28 at its opposite ends so as to be capable of shifting fore and aft below the stationary floor by means of link 31 which extends rearwardly to the ejection mechanism 30. The rolling door 27, as in the case of the stationary floor 26, is fabricated of rectangular tubes laid horizontally sideby-side with their longitudinal axes extending transversely of the scraper centerline.

Strike-off blade 32 has a blade frame 70 which extends transversely of the door 27 forwardly of the leading edge thereof. An angle 71 has an upper leg 72 extending laterally and a rear leg 73 extending downwardly. The leading edge of the rolling door 27 has a plurality of laterally spaced, transversely extending sleeve members 74 providing at the laterally spaced locations, hinge slots for the blade frame 70. A plurality of hinge lugs 75 are positioned in the hinge slots and aligned with the sleeve elements 74 so as to receive a horizontal hinge pin 76. A bottom plate 77 attaches to the rear leg 73 of the angle 71 and extends laterally upwardly to join adjacent the front edge of the upper leg 72 providing openings 79 along the leading edge for a row of bolts securing the strike-off blade element 80.

The end gate 24 may also be prefabricated of rectangular tubes in a manner similar to the other components. The end gate extends across the back of the body 16 (FIG. 1) between the side walls 25 and the slides on the stationary floor 26 between a retracted position in front of the cross beam 43 and a forward position adjacent the front edge of the stationary floor 26. The rolling door 27 and end gate 24 are operated in conjunction by the ejection mechanism 30 such that the rolling door is retracted and the end gate then pushed forwardly ejecting the earth material.

Referring to FIG. 6, an automatic welding set-up is depicted showing a side panel being welded. The panel is assembled on a traveling carrier 81 so as to be movable longitudinally below three automatic welding heads 82, one for each joint between the adjacent tubes of the side panel. The trackway channel 65 is shown already in place, however, it may be omitted at this step or included as part of the automatic welding process. Assuming that welding commenced at what would be the rear of the side wall on the exterior side, the welding heads are shown depositing the weld metal along fillet lines 33 extending in straight lines from the rear to the front of the side panel. Upon completion of one welding pass, the side panel is flipped over and welded on the interior side. Thus, one of the important advantages of the invention is secured by the provision of body components which lend themselves to automatic welding techniques. For example, as opposed to hand welding speeds of 5 or 6 inches per minute, the automatic welding heads 82 can deposit weld metal at the rate of about 40 inches per minute. Welding at the longitudinal edges of each tube produces a balanced weld about the neutral axis of each tube which reduces angular distortion in the panel practically to zero.

While I have described and illustrated herein a preferred embodiment of my invention as incorporated in a particular apparatus it will be appreciated that modifications may be made therein and that other uses may be found. Therefore, it should be understood that I intend to cover by the appended claims all such modifications as fall within the spirit and scope of my invention.

We claim:

1. A mobile scraper bowl comprising a body having a bottom wall and a pair of side wall structures extending upwardly from the bottom wall defining an earth material receiving space in said body, a plurality of tubular elements extending longitudinally parallel to each other in abutting side-byside relationship forming each side wall structure and being joined along interior and exterior straight line longitudinal weld locations to form a welded prefabricated panel, a cutting blade mounted between said panels at the forward ends and ground wheel support means carried partially by said panels.

2. A mobile scraper bowl according to claim 1 wherein the tubular elements are of rectangular cross sections such that the inner and outer wall segments of said panels form co-planar interior and exterior surfaces of said side walls.

3. A mobile scraper bowl according to claim 2 wherein the rectangular tubular elements are of substantially greater dimension vertically than transversely.

4. A mobile scraper bowl having a stationary bottom wall, side walls extending upwardly from and joined by the stationary bottom wall, a bottom opening forwardly of the stationary bottom wall, movable door normally closing said opening, rollers mounted at opposite ends of said door suspending the door for movement longitudinally below said stationary bottom wall, each said bottom and side walls being made of a prefabricated panel, each said panel being formed of a plurality of rectangular tubular elements extending longitudinally parallel to each other in abutting side-by-side relationship, said tubular elements each having spaced walls providing inner and outer co-planar surfaces which collectively define the interior and exterior surfaces of said panels, a cutting blade mounted between said panels, wheel support means carried partially by said panels and door operator means also carried partially by said panels for moving said door.

5. A mobile scraper bowl according to claim 4 wherein the panels forming said side walls have the tubular elements running longitudinally parallel to the centerline of the apparatus and the panel forming said stationary bottom wall has the tubular elements running transversely of the centerline.

6. An earth moving apparatus adapted to be towed by a tractor having a stationary bottom wall, side walls extending upwardly from and joined by the stationary bottom wall, a bottom opening forwardly of the stationary bottom wall, a movable door normally partially closing said opening, rollers at opposite ends of said door suspending the door for movement longitudinally below said stationary bottom wall, a yoke member pivotally supported on the tractor and having parallel arms extending rearwardly pivotally mounted on the side walls supporting said apparatus for articulation relative to the tractor, a fixed main blade mounted between the side walls forwardly of said opening, a pivoted blade member hinged on the front of said door and cooperating with the main blade and door in the forward position of the latter to completely close said opening and being pivoted downwardly when said door opens for spreading earth material dumped through said opening, each of said side walls being made of a prefabricated panel, each said panel being formed of a plurality of tubular elements extending longitudinally parallel to each other in abutting side-by-side relationship, the tubular elements having spaced walls providing inner and outer surfaces collectively defining the interior and exterior surfaces of said panels, the lowermost tubular element of each side panel having a longitudinally extending cut-out forming diametrically opposed openings in the lower outer surface of the side walls, a pair of channel elements, each having a web and parallel longitudinally extending legs joined to the web, one channel element fitting within the cut-out of one panel and the other channel element fitting within the cut-out of the opposite panel and said channel elements cooperating in the assembled side walls to provide longitudinally parallel trackways for guiding the door support rollers.

7. An earth moving apparatus according to claim 6 wherein the leading and trailing ends of the tubular elements in said panels define the front and rear ends of the assembled side walls.

8. An earth moving apparatus according to claim 7 wherein a plate closes the open ends of a plurality of said tubular elements at the leading and trailing ends of each panel to close the front and rear ends of the side walls.

9. An earth moving apparatus according to claim 7 wherein the upper and lower tubular elements in each side wall panel are shorter at the leading ends than the intermediate tubular elements providing upper and lower diametrically opposed openings in said assembled side walls, structural means for pivotally supporting the ends of said yoke arms received in said upper openings and structural blade support means for supporting the opposite ends of said main blade received in said lower openings.

10. An earth moving apparatus according to claim 9 wherein said main blade includes, a blade support frame, said blade support frame comprising a tubular element spaced from and extending parallel to the leading edge of the main blade, said tubular element having spaced upper and lower walls, a top plate extending lengthwise of the tubular element secured to said upper wall and extending laterally thereof, a bottom plate extending lengthwise of the tubular element joined to the lower wall and extending laterally thereof on an angle joining at the outer end with said upper plate, said upper plate providing at its outer edge a main blade support surface for removably mounting a blade element and said tubular element and top and bottom plates being in close abutting relationship to said structural blade support means and defining therewith generally straight line peripheral weld locations around said blade support frame.

11. An earth moving apparatus according to claim 10 wherein the tubular element of the blade support frame has spaced front and back walls and the leading ends of the lower tubular element in said side panels incline rearwardly cooperating with the back wall of said tubular element of the blade support frame to establish the angle of said main blade for proper engagement with the ground.

12. An earth moving apparatus according to claim 6 wherein said pivoted blade member hinged on the front of said door includes a pivoted blade support frame comprising a first transversely extending structural element having an upper leg portion extending laterally and a rear leg portion extending downwardly, said door being formed of a plurality of tubular elements extending transversely of the apparatus, a transversely extending sleeve member across the leading edge of said door, laterally spaced hinge locations for said pivoted blade support frame formed in said sleeve member, a plurality of hinge lugs laterally spaced on the rear of said structural element projecting rearwardly of said leg portions being received in said laterally spaced hinge location, and hinge pintle means received in said sleeve member for hinging the pivoted blade support frame on to said door.

13. An earth moving apparatus according to claim 12 wherein a pair of end plates, one at each end of said pivoted blade support frame are in abutting relationship with said structural element defining with said leg portions straight line peripheral weld locations for securing the end plates.

i t i k 

1. A mobile scraper bowl comprising a body having a bottom wall and a pair of side wall structures extending upwardly from the bottom wall defining an earth material receiving space in said body, a plurality of tubular elements extending longitudinally parallel to each other in abutting side-by-side relationship forming each side wall structure and being joined along interior and exterior straight line longitudinal weld locations to form a welded prefabricated panel, a cutting blade mounted between said panels at the forward ends and ground wheel support means carried partially by said panels.
 2. A mobile scraper bowl according to claim 1 wherein the tubular elements are of rectangular cross sections such that the inner and outer wall segments of said panels form co-planar interior and exterior surfaces of said side walls.
 3. A mobile scraper bowl according to claim 2 wherein the rectangular tubular elements are of substantially greater dimension vertically than transversely.
 4. A mobile scraper bowl having a stationary bottom wall, side walls extending upwardly from and joined by the stationary bottom wall, a bottom opening forwardly of the stationary bottom wall, movable door normally closing said opening, rollers mounted at opposite ends of said door suspending the door for movement longitudinally below said stationary bottom wall, each said bottom and side walls being made of a prefabricated panel, each said panel being formed of a plurality of rectangular tubular elements extending longitudinally parallel to each other in abutting side-by-side relationship, said tubular elements each having spaced walls providing inner and outer co-planar surfaces which collectively define the interior and exterior surfaces of said panels, a cutting blade mounted between said panels, wheel support means carried partially by said panels and door operator means also carried partially by said panels for moving said door.
 5. A mobile scraper bowl according to claim 4 wherein the panels forming said side walls have the tubular elements running longitudinally parallel to the centerline of the apparatus and the panel forming said stationary bottom wall has the tubular elements running transversely of the centerline.
 6. An earth moving apparatus adapted to be towed by a tractor having a stationary bottom wall, side walls extending upwardly from and joined by the stationary bottom wall, a bottom opening forwardly of the stationary bottom wall, a movable door normally partially closing said opening, rollers at opposite ends of said door suspending the door for movement longitudinally below said stationary bottom wall, a yoke member pivotally supported on the tractor and having parallel arms extending rearwArdly pivotally mounted on the side walls supporting said apparatus for articulation relative to the tractor, a fixed main blade mounted between the side walls forwardly of said opening, a pivoted blade member hinged on the front of said door and cooperating with the main blade and door in the forward position of the latter to completely close said opening and being pivoted downwardly when said door opens for spreading earth material dumped through said opening, each of said side walls being made of a prefabricated panel, each said panel being formed of a plurality of tubular elements extending longitudinally parallel to each other in abutting side-by-side relationship, the tubular elements having spaced walls providing inner and outer surfaces collectively defining the interior and exterior surfaces of said panels, the lowermost tubular element of each side panel having a longitudinally extending cut-out forming diametrically opposed openings in the lower outer surface of the side walls, a pair of channel elements, each having a web and parallel longitudinally extending legs joined to the web, one channel element fitting within the cut-out of one panel and the other channel element fitting within the cut-out of the opposite panel and said channel elements cooperating in the assembled side walls to provide longitudinally parallel trackways for guiding the door support rollers.
 7. An earth moving apparatus according to claim 6 wherein the leading and trailing ends of the tubular elements in said panels define the front and rear ends of the assembled side walls.
 8. An earth moving apparatus according to claim 7 wherein a plate closes the open ends of a plurality of said tubular elements at the leading and trailing ends of each panel to close the front and rear ends of the side walls.
 9. An earth moving apparatus according to claim 7 wherein the upper and lower tubular elements in each side wall panel are shorter at the leading ends than the intermediate tubular elements providing upper and lower diametrically opposed openings in said assembled side walls, structural means for pivotally supporting the ends of said yoke arms received in said upper openings and structural blade support means for supporting the opposite ends of said main blade received in said lower openings.
 10. An earth moving apparatus according to claim 9 wherein said main blade includes, a blade support frame, said blade support frame comprising a tubular element spaced from and extending parallel to the leading edge of the main blade, said tubular element having spaced upper and lower walls, a top plate extending lengthwise of the tubular element secured to said upper wall and extending laterally thereof, a bottom plate extending lengthwise of the tubular element joined to the lower wall and extending laterally thereof on an angle joining at the outer end with said upper plate, said upper plate providing at its outer edge a main blade support surface for removably mounting a blade element and said tubular element and top and bottom plates being in close abutting relationship to said structural blade support means and defining therewith generally straight line peripheral weld locations around said blade support frame.
 11. An earth moving apparatus according to claim 10 wherein the tubular element of the blade support frame has spaced front and back walls and the leading ends of the lower tubular element in said side panels incline rearwardly cooperating with the back wall of said tubular element of the blade support frame to establish the angle of said main blade for proper engagement with the ground.
 12. An earth moving apparatus according to claim 6 wherein said pivoted blade member hinged on the front of said door includes a pivoted blade support frame comprising a first transversely extending structural element having an upper leg portion extending laterally and a rear leg portion extending downwardly, said door being formed of a plurality of tubular elements extending transversely of the apparAtus, a transversely extending sleeve member across the leading edge of said door, laterally spaced hinge locations for said pivoted blade support frame formed in said sleeve member, a plurality of hinge lugs laterally spaced on the rear of said structural element projecting rearwardly of said leg portions being received in said laterally spaced hinge location, and hinge pintle means received in said sleeve member for hinging the pivoted blade support frame on to said door.
 13. An earth moving apparatus according to claim 12 wherein a pair of end plates, one at each end of said pivoted blade support frame are in abutting relationship with said structural element defining with said leg portions straight line peripheral weld locations for securing the end plates. 